pastix: fix dynamic linking of examples
pastix: fix dynamic linking of examples

By default, the examples are linked against the libraries in the build
directory, that will be gone once the installation completes. Link them
against the just installed libraries instead, so they can be used even
after the installation, e.g., in `brew test`.

maplesond/homebrew-science,ahundt/homebrew-science,dpo/homebrew-science,goxberry/homebrew-science,pmelsted/homebrew-science,philippbayer/homebrew-science,ge11232002/homebrew-science,andrewjpage/homebrew-science,parcollet/homebrew-science,pditommaso/homebrew-science,DabeDotCom/homebrew-science,quantumsteve/homebrew-science,joshbode/homebrew-science,kozo2/homebrew-science,aeantipov/homebrew-science,heuermh/homebrew-science